Double-fed asynchronous machines with a power range of from 20 MVA to 500 MVA can be used for variable-speed energy production. These machines are characterized by a distributed three-phase winding on the rotor. The rotor winding comprises individual bars which are embedded in slots in the rotor laminate stack. The bars are interconnected to form a winding in the end winding. The currents are fed via at least three slip rings, which are fastened on the rotor shaft at the end of the machine. A detail of such a machine is shown in FIG. 1 in a very simplified form. The asynchronous machine 10 illustrated in FIG. 1 has a machine axis 19. A central core 11 comprising a shaft 11a on which the slip rings 17 are arranged is rotatable about this axis 19. The rotor laminated core 12 is arranged around the central core 11, with an auxiliary rim 13 adjoining said rotor laminated core beneath an end winding 14 of the rotor winding. The rotor laminated core 12 is surrounded concentrically by a stator laminated core 15, in which a stator winding is accommodated which protrudes outwards at the end of the core 15 with a stator end winding 16.
The three phases of the rotor winding need to be connected to the slip rings 17 at the end of the shaft 11a. For this purpose, conductors (not illustrated) are accommodated in the shaft 11a, which conductors are connected firstly to the slip rings 17 and secondly to the end windings 14 at the level of the ends of the end windings. The connectors 18 (indicated by dashed lines in FIG. 1) passing at right angles to the shaft need to be insulated for the rotor test voltage. The connectors 18 carry the rated rotor current and in this case should not exceed the required limit temperature. The system of connectors 18 needs to be sufficiently flexible in the axial direction (at the connection point of the winding) and in the radial direction to enable the thermal expansion of the winding in the axial direction and the expansion of the rotor core in the radial direction to be accommodated. Finally, the connectors 18 need to be safeguarded with respect to the high centrifugal forces.